How to Check whether Session is Expired or not in asp net

Question

I ve specified the session timeout in web config file  When the session is timeout I m not getting redirect to the login page but I am getting an error saying object reference not set to an instance   Can anyone tell me the solution for this

User · Answer

I prefer not to check session variable in code instead use FormAuthentication. They have inbuilt functionlity to redirect to given LoginPage specified in web.config.

However if you want to explicitly check the session you can check for NULL value for any of the variable you created in session earlier as Pranay answered.

You can create Login.aspx page and write your message there , when session expires FormAuthentication automatically redirect to loginUrl given in FormAuthentication section

<authentication mode="Forms">
  <forms loginUrl="Login.aspx" protection="All" timeout="30">
  </forms>
</authentication>

The thing is that you can't give seperate page for Login and SessionExpire , so you have to show/hide some section on Login.aspx to act it both ways.

There is another way to redirect to sessionexpire page after timeout without changing formauthentication->loginurl , see the below link for this : http://www.schnieds.com/2009/07/aspnet-session-expiration-redirect.html

User · Answer

Edit  You can use the IsNewSession property to check if the session was created on the request of the page  protected void Page Load          if  Context Session    null               if  Session IsNewSession                     string cookieHeader   Request Headers  Cookie              if   null    cookieHeader   amp  amp   cookieHeader IndexOf  ASP NET SessionId    gt   0                            Response Redirect  sessionTimeout htm                                    pre  Store Userid in session variable when user logs into website and check on your master page or created base page form which other page gets inherits  Then in page load check that Userid is present and not if not then redirect to login page   if Session  Userid    null        session expire redirect to login page

User · Answer

You can check the HttpContext Current User Identity IsAuthenticated property which will allow you to know whether there s a currently authenticated user or not

User · Answer

Use Session Contents Count   if  Session Contents Count    0        Response Write   NET session has Expired        Response End      else       InitializeControls        The code above assumes that you have at least one session variable created when the user first visits your site  If you don t have one then you are most likely not using a database for your app  For your case you can just manually assign a session variable using the example below    protected void Page Load object sender  EventArgs e        Session  user id     1      Best of luck to you

User · Answer

I use the  Adi-lester answer and add some methods    Method to verify if Session is Alive  public static void SessionIsAlive HttpSessionStateBase Session        if  Session Contents Count    0                Response Redirect  Timeout html               else               InitializeControls              Create session var in Page Load  protected void Page Load object sender  EventArgs e        Session  user id     1      Create SaveData method  but you can use it in all methods   protected void SaveData            Verify if Session is Alive     SessionIsAlive Session          Save Data Process        bla        bla        bla

User · Answer

Here I am checking session values two values filled in text box on previous page       protected void Page Load object sender  EventArgs e        if  Session  sessUnit code      null    Session  sessgrcSerial      null                Response Write   lt Script Language    JavaScript  gt  alert  Go to GRC Tab and fill Unit Code and GRC Serial number first   lt  script gt               else                lblUnit Text   Session  sessUnit code   ToString            LblGrcSr Text   Session  sessgrcSerial   ToString

User · Answer

this way many people detect session has expired or not  the below code may help u   protected void Page Init object sender  EventArgs e                if  Context Session    null                        if  Session IsNewSession                                HttpCookie newSessionIdCookie   Request Cookies  ASP NET SessionId                    if  newSessionIdCookie    null                                        string newSessionIdCookieValue   newSessionIdCookie Value                      if  newSessionIdCookieValue    string Empty                                                   This means Session was timed Out and New Session was started                         Response Redirect  Login aspx

User · Answer

Check if it is null or not e g  if Session  mykey      null         Session is not expired   else       Session is expired

[c#] How to Check whether Session is Expired or not in asp.net

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